Tunnel kiln and method of operating same



Aug. 19 1924. 1,505,767

' P. D H. DRESSLER TUNNEL KILN AND METHOD OF OPERATING sum Original Filed July 9. 1926 2 Sheets-Sheet 1 Aug. 19, 1924.

1,505,767 P. DH. DRESSLER TUNNEL KILN AND METHOD OF OPERATING SAME Original Filed July 9. 1920 2 Sheets-Sheet 2 All m Patented Aug. 19, 1924.

UNITED STATES PATENT OFFICE.

PHILIP DH. DRESSLER, OF ZANESVIIILE, OHIO, ASSIGNOR TO AMERICAN DRESSLER TUNNEL KILNS, INC., 0]? NEW YORK, N. Y., A CORPORATION OF NEW YORK.

. TUNNEL KILN .AND METHOD OF OPERATING SAME.

Application filed July 9, 1920, Serial No. 394,985. Renewed September 12, 1923.

To all whom it may concern.

Be it known that I, PHILIP DH. Dnnss- LER, a subject of the King of Great Britain, and resident of Zanesville, in the county of Muskingum and State of Ohio, have in vented certain new and useful Improvements in Tunnel Kilns and Methods of Operating Same, of which the following is a specification.

A primary object of the present invention is to provide for an improved regulation of temperature conditions in the zone of a continuous tunnel kiln traversed by the ware after passing through the zone in which the highest kiln temperatures are maintained especially adapted to secure a slow and even cooling of the ware in the certain stages of the cooling operation.

In the usual type of tunnel kiln heat is abstracted from the kiln cooling zone along the entire length of the kiln by means of a cooling fluid flowing lengthwise of the kiln through the kiln chamber itself or through special cooling conduits the direction of flow being opposite to the direction of travel of the ware. In addition to the heat abstracted from the ware by the cooling fluid some heat is transmitted from the ware to the kiln walls and dissipated from the latter into the external atmosphere.

I have discovered that in some cases as in annealing malleable castings where a very slow and even cooling is desired, that instead of abstracting heat from the kiln by the use of a circulating cooling fluid, it may be desirable to impartsome heat to the kiln in its cooling zone portion to partially compensate for the natural heat losses therefrom. This I accomplish in accordance with the present invention by providing for the flow of a heating agent lengthwise of an initial portion of the cooling zone of the kiln with the direction of flow the same as the direction of travel of the ware. In the preferred arrangement of carrying out my invention I provide means for causing this flow when conditions require it and for causing a flow in the reverse direction of a cooling fluid when conditions make desirable a more rapid abstraction of heat from the ware.

In some annealing operations carried out in continuous tunnel kilns it is highly desirable that the articles being annealed should not be exposed to a. highly active oxidizing atmosphere while at a temperature high enough. to result in surface oxidation, and my invention also comprises a novel arrangement for supplying products of combust-ion to the kiln chamber to make the atmosphere therein neutral or at least to prevent it from being highly oxidizing.

The various features of novelty which characterize my invention are pointed out with particularity in the claims annexed to and forming a part of this specification. For a better understanding of the invention. however, and the advantages possessed by it, reference should be had to the accompanying drawings and descriptive matter in which I have illustrated and described a preferred embodiment of my invention.

Of the drawings;

Fig. 1 is a diagrammatic plan view with parts broken away and in section of a kiln.

Fig. 2 is a longitudinal sectional elevation of the apparatus shown in Fig. 1.

F ig. 3 is a transverse section taken on the line 3-3 of Fig. 1.

Fig. 4 is a temperature curve;

Fig. 5 is an elevation of a portion of the apparatus shown in Fig. 1; and

Fig. 6 is a diagrammatic view of another form of kiln in which my invention is used.

In the drawings, and referring first to the construction shown in Figs. 15, I have illus- (rated the use of my invention in connection with a continuous tunnel kiln of the Dressler type especially devised for use in annealing malleable castings. The horizontally elongated kiln chamber A is provided at its entrance end with an antechamber A, and at its exit end with an exit chamber A Doors E are provided at the opposite ends of the antechamber and exit chamber. The articles to be annealed are moved slowly through the kiln on the usual kiln cars F which form a train extending through the kiln, cars being pushed into the kiln from the antechamber A, at regular intervals, the train of cars in the kiln being advanced a car length each time a car is inserted, and a car being removed from the kiln chamber A to the exit chamber A each time a car is inserted. The kiln chamber A comprises a heating up zone B, an. intermediate initial cooling zone C, and .a final cooling zone D. The arrangement of these zones employed in one embodiment of my invention already in use is ot the kiln chamber.

shown by Fig. 4. The temperature curve Z in Fig. 4: illustrates variations in temperature at ditl'erent points along the kiln length which may be maintained in this particular kiln.

COITIblIStlOl] chambers G extend longitudinally of the zone I?) and are arranged one at each side of the pathway for the goods being supported on masonry benches A as is usual in Dressler kilns. Advant-ageously, as shown, each combustion chamber G is formed with channels G in its walls extending transversely to the length of the combustion chamber as set forth in the patent to Conrad Dressler #LlTOAZS. These passages insure a direct gravity circulation of the kiln atmosphere upward through the combustion chamberchannels G and downward through the pathway for the goods. Fuel, and air for its comlnistion, are supplied to each combustion chamber G at burner inlets H distributed along the portion of the combustion chamber remote from the ante chamber. As shown the air to support combustion is supplied by air supply conduits I, and the air thus passed to the burner inlets is preheated by its passage through a recuperatm' J to which atmospheric air is supplied by the discharge pipe K of one or more blowers K. Fuel, which may be gas or oil, is supplied to each burner inlet H through a corresponding branch pipe N from fuel mains N. Products of combustion are withdrawn from the combustion chambersG at the exit ends of the latterthrough valved outlets 1 openings. as sl1own, into passages L, formed in, the benches A and leading to a duct l) running to the recupcrator J. The products of combustion after being more or less cooled. by their passage through the recuperator J are withdrawn from the latter through a con duit M running to a suitable draft creating device. i

In the intermediate zone C of the lciln, mufl'lcs or conduits GA are located, one on each of the benches A". As shown, the conduits GA extend the full. length of this zone The conduits GA are shown as identical in construction with the combustion chambers G already described. To permit of the combustion of fuel in the conduits GA when this is necessary, each ('fOlltlHit GA is provided adjacent its end nearest the zone B, with one or more burner inlets HA. The burner inlets HA are supplied with preheated air from the piping I and with fuel from the piping M exactly as are the burner inlets H for the combustion chambers G. At its end adjacent the zone B, each. conduit GA is provided with an outlet 0, flow through which is controlled by a damper or valve 0. The outlets O are connected to a duct 0 running to a suitable draft creating device which, as shown, is a,

stack 0 Each of the chambers GA. is provided at its end, remote from the zone B with an outlet P, flow through which may be controlled by a damper P The latter is connected to apparatus, hereinafter described, by means of which air may be passed into, or products of combustion may be drawn out of the conduits GA through the passages l i\lounted on the benches A in the cooling yone ot the kiln are cooling pipes R connected at their ends to headers R and R The headers R which are adjacent the exit end of the kiln receive atmospheric air in any suitable manner, as through ports R formed in the kiln walls. The headers R are connected by outlet passages S, each of which may advantageously be provided with a controlling valve or damper S to a duct S leading to a suitable draft creating device for drawing air at the desired rate through the pipes R. As shown, the two ducts l and S which are arranged side by side, are connected by a hood PS. The hood PS, as shown, is connected to the inlets of two exhaust fans Q and. T. and T" are provided for disconnecting either tan Q, or T "from the hood PS. The fan Q has its outlet connected to a stack Q}, and the fan T has its outlet connected to a stack T In the preferred construction illustrated, the outlet M from the recuperator J is connected to the inlets of two exhaust fans V and VA connected through a corresponding outlet V to a. stack W Either of the exhaust tans V and VA may be disconnected troin the pipe M by closing a. corresponding damper or valve V. The outlet V from, the tan V is connected by a pipe X running to the ante chamber A, and the outlet V from the tan V A is connected by a conduit X.\ to the exit chamber A of the kiln. The conduits X and XA are each provided with a regulating damper X, and the stack \V is provided with a damper TV. By adjusting the dampers X. and W the products of coinlnistion drawn from the recuperator J bv either or both of the exhaust fans V and. VA may be passed in any desired relative proportions to the ante chamber A, the exit chamber A and out through the stack TV. It will be understood that functionally, the tans V and VA are duplicates, either of which may be cut out of service without destroving the capacity of the plant to operate in the same manner as when both are in service. .In practice one of these fans normally serves as a spare, while the other is in regular operation. and this is true also of the two blowers K and the two exhaust fans Q, and T.

In the regular intended operation of the apparatus shown, fuel and air for its combustion are supplied to the combustion Dampers Q" chambers G at the rate required to heat the articles being annealed from their entrance temperature to the temperature indicated by the point Z in the temperature curve Z of Fig. 4-, during the passage of the articles through the heating up zone A of the kiln. In passing through the kiln zone C the articles are maintained at a relatively high temperature, as shown in Fig. 4, the temperature falling but slightly in the zone Cr \Vhether heat must be supplied to or abstracted from the zone C of the kiln will depend in part upon the exact character of the temperature curve desired between the points Z and Z at the ends of the zone, and partly upon the rate at which heat is lost by radiation and otherwise from this portion of the kiln. The apparatus described permits heat to be supplied by the conduits GA, or abstracted by the latter. W hen the conduits GA are to supply heat to the zone C, fuel and air for its combustion are supplied to the conduits GA at the inlets HA, and the resultant products of combustion are drawn off through the outlets P. In

this condition of operation, the dampers O are closed and the duct P is connected by the corresponding exhaust fan Q, or T to one of the stacks Q and T hen heat is t "be abstracted from the kiln zone C by the conduits GA, the dampers O are opened to connect the corresponding ends of the conduits GA to the stacks O and the dampers Q and T are so regulated that more or less of the air flowing through the cooling zone pipes R will pass from the duct S through the hood BS into" the duct I and thence through the passages I into the conduits GA. 1

It will be observed that when the conduits GA supply heat to the kiln chamber the direction of flow through the conduits GA is longitudinally of the kiln in a direction opposite to that of the flow through the combustion chambers G. WVhen the conduits GA are to abstract heat from the kiln chamber the flow through these conduits is in the same direction as the flow through the combustion chambers G. lVith either direction of flow through each conduit GA, however, the fluid passing through the conduit GA will be hotter at the end f the conduit adjacent the combustion chambers G, than at its opposite end. This is as it should be, to give a temperature curve of the general character indicated in Fig. 4. By making the conduits GA similar in construction to the combustion chambers G, a directed convection current circulation of the kiln atmosphere is obtained through the channels G of the conduits GA when these conduits are abstracting heat from the kiln chamber, as well as when they are giving heat to the kiln chamber, though when abstracting heat the flow through the channels G will be downward and not upward. This directed convection current circulation adds t the efliciency of the heat transfer and tends to equalize the temperatures at different levels in the kiln chamber.

\Vhile I prefer to employ a muflie heated kiln of the general character illustrated. the

temperature regulation in the intermediate zone of the kiln characterizing the present invention may be obtained in a kiln of the open fire type as shown somewhat diagrammatically, for example, in Fig. 6. The kiln shown in Fig. 6 comprises a heating zone BA, a final cooling zone DA and an intermediate zone CA. The heating zone BA is heated by means of burners HA which open to the kiln chamber at the exit or tail end of the zone AB and receive fuel through the piping NA. The products of combustion are drawn through the kiln chamber to the entrance end of the latter by a suitable draft creating device shown as a stack X connected to the kiln chamber at A The final cooling zone DA of the kiln is cooled by air. As shown the air is drawn through the kiln chamber from the exit end of the latter by a fan Y which is connected to the kiln chamber at A Advantageously, as shown, some or all of the air drawn through the cooling zone DA is passed from the fan Y to the heating burners HA through the pipes IA. IA represents a branch discharge-pipe through which some of the air delivered by the fan Y may be diverted to other uses or discharged into the atn'iosphere. An exhaust fan Z opening to the kiln chamber at A adjacent but toward the entrance end of the kiln from the outlet A- forms a. means by which hot gases may be drawn through the zone CA ot the kiln chamber when this is desirable.

The hot gases thus drawn through the zone CA may be a portion of the burning gases from the burners HA or may come from special burners HA also receiving fuel and air from the piping NA and IA.

WVith the construction shown in Fig. 6 it is possible, as by the use of suitable dampers IV, to regulate the relative suction effects impressed on the outlets A A and A so as to draw as much or as little of the burning gases from the burners HA and HA through the zone CA as may be desired, or to cause a flow through the zone CA of air from the final cooling zone DA to the heating zone BA through the kiln zone CA. The openings A, A and A for drawing off exhaust gases and heated air are shown centrally but it must be understood that they may be placed at any other convenient spot.

Certain generic features of my invention disclosed in common in this application and in my copending application, Serial No.

653,892, filed July 26, 1923, and not claimed herein are claimed in said copending application.

While, in accordance with the provisions of the statutes, I have illustrated and described the best form of my invention now known to me, it will be apparent to those skilled in the art that changes may be made in the form of the apparatus disclosed without departing from the spirit of my invention, as set forth in the appended clain'is and that certain features of my invention may sometimes be used to advantage without a corresponding use of other f natures.

Having now described my invention, what I claim as new and desire to secure by Letters Patent. is:

1. In a continuous tunnel kiln, the combination with the kiln chamber, of means for supplying heat to a heating up and high temperature zone of the kiln chamber and means for regulating the temperature in another zone of the kiln chamber comprising conduits extending along said last mentioned zone, and means for passing either a heating medium or a cooling medium through said conduits.

2. The method of operating a continuous tunnel kiln comprising a heating zone at one end of the kiln. a final cooling zone at the opposite end of the kiln and an intermediate zone which consists in passing a heating fluid through the intern'iediate zone in one direction when it is desired to impart heat to that zone and in passing a cooling fluid through the zone in the opposite direction when it is desired to abstract heat from the zone.

3. In a continuous tunnel kiln, the combination with the kiln chamber, of inulllc heatingineans for supplying heat to a heating up and high tQlI'lI'JCIittlll'G zone of the kiln chamber and means for regulating the temperature in another zone of the kiln chamber comprising conduits extending along said last mentioned zone, and means for passing either a heating medium or a cooling medium through said conduits.

4. In a continuous tunnel kiln comprising a heating up section, a cooling section and an intermediate section; the combination with the kiln chamber of a conduit extendingalong the intermediate section of the kiln and provisions for passing a heating fluid through the conduit in one direction or a cooling fluid through the conduit in the opposite. direction to supply heat to or abstract it from said intermediate section as desired.

5. In a continuous tunnel kiln, the combination with the kiln chamber, of combustion chambers placed end to end therein, and means for supplying fuel and air for its combustion to the end of each combustion chamber adjacent the other combustion chamber and for withdrawing products of combustion from the combustion chambers at their remote ends.

6. In a continuous tunnel kiln the combination with the kiln chamber and a combustion chamber therein extending along a heating up zone section of the kiln, of another combustion chamber in an adjacent section of the kiln, means for supplying fuel and air for its combustion to one end of said other combustion chamber and for withdrawingproducts of combustion from heating means therefor, of an external re-.

cuperator and means for withdrawing products of combustion from the heating means through said recuperator and then passing them back into the kiln.

8. In a continuous tunnel kiln the combination with the kiln chamber and muffle heating means therefor, of an external recuperator and means for withdrawing products of combustion from the mullle heating means through said recuperator and then passing them back into the kiln chamber.

9. In a continuous tunnel kiln the combination with the kiln chamber and mutlie heating means therefor, of means for withdrawing products of combustion from the muflle heating means and then passing them back into the kiln chamber.

Signed at New York, in the county of New York and State of New York, this 8th day ofJuly, A. D. 1920.

PHILIP nH. DRESSLER. 

